The two most common operations in the practice of drafting are the scribing of horizontal and vertical lines relative to the orientation of the drafting work or drawing. Horizontal lines are generally produced with the use of a T-square or horizontal bar, and vertical lines are generally produced with the use of a right triangle in conjunction with a T-square or horizontal bar. Such triangles are also generally used to produce lines at the commonly needed angles of 30 degrees, 45 degrees, or 60 degrees from the horizontal, and are commonly available in 30-60 degree and 45 degree models. Despite their almost universal use, such triangles are subject to several disadvantages and problems, especially when used for the production of vertical lines.
The majority of those problems stem from the full contact between the extensive surface area of the face of the triangle and the drawing surface and the difficulty of grasping a triangle which is flat upon the drawing surface in order to flip it from face to face. The full contact between the face of the triangle and the drawing surface often produces smearing of both graphite or ink lines on the drawing if the triangle is slid over those lines, so it is necessary for the draftsman to position the triangle so that it is not disposed directly over at least the most recently performed work. This necessity often creates strained working positions and reduces the efficiency of the draftsman.
In addition, the use of graphite pencils and the use of erasers leaves graphite and eraser residue on the drafting surface, which accumulates along the working edge of the T-square or horizontal bar at the surface of the drawing. As a triangle is slid along that edge of the horizontal bar the edge of the triangle is in contact with the residue, increasing the drag between the contiguous edges of the two instruments and increasing the probability of creating graphite smears on the drawing surface.
Various approaches to solution of these problems have been attempted and are known in the prior art, but none of the approaches have fully addressed the combination of problems, and none have presented a coordinated solution. L-shaped drafting instruments are known in the art, as illustrated by British Pat. No. 386,883 and French Pat. No. 730,763. Those instruments are, however, primarily directed to the purpose of providing an instrument capable of creating certain specific angles or scribing lines of a certain specific length. Similarly, various triangle designs have been proposed, such as those illustrated by U.S. Pat. No. 482,023 and U.S. Pat. No. 4,545,130, for the primary purpose of providing an instrument capable of creating a multiplicity of different angles and curves.
French Pat. No. 1,385,756 discloses the use of raised points on the face of a T-square or triangle to raise the instrument above the surface of the drafting work, which alleviates certain of the normal disadvantages of the use of a triangular instrument, but the design stops short of a coordinated solution to the full scope of problems associated with a triangular instrument.
The use of a handle extending outwardly from at least one face of a drafting instrument has also been previously proposed, as in U.S. Pat. No. 831,314, U.S. Pat. No. 699,738, and U.S. Pat. No. 2,364,529. These designs are useful in providing a means of more readily grasping the drafting instrument with which they are used, but again do not address the full scope of problems.
It is an object of the present invention to provide a fully coordinated approach to solution of the problems associated with the use of a standard drafting triangle, and it is a further object of the present invention to provide a drafting instrument with a combination of features directed to performance of drafting work in a highly efficient manner.